Method and system of bi-directional transmission to improve uplink performance

ABSTRACT

In coverage enhancement of machine type communication (MTC), a downlink transmitted bit stream is jointly encoded with uplink payload by the terminal. The combined signal is sent on uplink, to be jointly decoded by the base station that knows the downlink payload and the joint encoding mechanism at the mobile terminal.

FIELD OF THE INVENTION

The present invention relates to a method and system of hi-directionaltransmission between a base station and a terminal to improve uplinkperformance, and to the use of network coding between downlink anduplink,

BACKGROUND OF THE INVENTION

Machine type communication (MTC) is considered as one of the majordriving forces of a future generation of cellular communications. Likelyapplication scenarios for MTC feature numerous low-cost machine-typedevices connecting to the network. The data packet size of MTC isusually smaller than that of human-to-human cellular communications.Because of the smaller data packet sizes, iterative types of channelcodes such as turbo codes or low density parity check (LDPC) codes wouldprovide less coding gain with MTC than is usual with the longerhuman-to-human packet sizes. To make the matter worse, some types of MTCdevices, like meter reading for utilities, are often installed in abasement or other area with poor signal penetration, which requires asuperb link budget to overcome the deep penetration loss.

Coverage enhancements can be achieved in several ways. One approach isto use CDMA-like signals that have lower peak to average ratio, lesscontrol overhead, etc. A second approach is to use more antennas, eitherat the transmitter with beamforming or to obtain transmit diversitygain, or at the receiver to obtain aperture or receive diversity gain. Athird approach is repetition, which has been used in 3GPP LTE, for thereason that LTE is an OFDMA system and there is no compelling reason tooverhaul that fundamental just for the sake of coverage. Note thattransmission time interval (TTI) bundling enhancements, as described inY. Yuan, et al, “LTE-Advanced coverage enhancements,” IEEE Comm. Mag.October, 2014, pp, 153-159, as one type of repetition, are alreadyspecified in Rel-11 LTE for uplink Voice over IP (VoIP) and data trafficcarried on physical uplink shared channel (PUSCH). In Rel-12 and Rel-13LTE, repetition is believed to the most effective technique to achievegood coverage of narrow-band MTC and has been extended to many otherphysical channels, for example, primary broadcast channel (PBCH),physical downlink shared channel (PDSCH), enhanced physical downlinkcontrol channel (EPDCCH), etc.

Network coding has attracted attention as an academic research topic.Its most promising use scenarios include relay, mesh networks, anddevice to device (D2D) communications.

Network coding takes advantage of the broadcast nature of wirelesscommunications, and can make use of not-directly targetedtransmission(s) to improve the redundancy of transmissions in acoordinated manner.

Significant impact on standards is expected if network coding is to beadopted in LTE. Since the channel coding would remain largely unchangedin LTE/LTE-A, network coding, which inevitably affects the channelcodes, has not been studied in 3GPP LTE.

SUMMARY

In accordance with one aspect, there is provided a method oftransmitting one or more signals in a downlink message for multiplemobile terminals to receive, and then each terminal, upon successfuldecoding of one or more of the one or more signals, incorporatesinformation carried in the downlink signals into its own informationbits to be sent in an uplink message. The method comprises twoprocesses, performed in the downlink and the uplink, respectively. Thefirst process involves a downlink transmission in which information canbe sent from a base station either in broadcast mode or in user-specificmode. The second process concerns the integration between theinformation sent by the base station and the terminal's own information,to form a jointly coded bit stream for uplink transmission.

In an embodiment, the information carried in the downlink transmissioncan be common to all the terminals being served by the base station. Thecommon information is sent in the broadcast mode, with the same IDcommon to all the terminals.

In an embodiment, the information carried in the downlink transmissioncan be user-specific so that different terminals would receive differentinformation. Different terminals may also receive different sizepayloads of information.

In an embodiment, the user-specific message is transmitted in adedicated channel, which makes it possible for any or all of the signalformat, channel coding and occupied time-frequency-spatial resourcestargeted to each mobile terminal to be different from others.

In an embodiment, the integration of the downlink information payloadand the uplink. information payload can result in a combined bit streamof the same size as the original uplink information payload. In thatembodiment, the downlink bits are effectively completely absorbed in theuplink bit stream.

In another embodiment, the integration of the downlink informationpayload and the uplink information payload can result in a combined bitstream of larger size than the original uplink information.

In another aspect, there is provided a system that involves a basestation transmitting one or more signals in the downlink for multiplemobile terminals to receive, and then each terminal upon successfullydecoding one or more signals, would incorporate the information carriedin the downlink into its own information bits to be sent in the uplink.The system implements two processes, performed in the downlink and theuplink, respectively. The first process involves downlink transmissionin which the carried information can be sent from base station in eitherbroadcast mode or user-specific mode. The second process concerns theintegration between the information sent by the base station, and theterminal's own information, to form a jointly coded bit stream foruplink transmission.

In another aspect, there are provided terminals, base stations, computerprograms and other machine-readable instructions, and non-volatilecomputer-readable storage media containing such instructions, forputting the methods and systems into effect.

The foregoing and other features and advantages will become moreapparent in light of the following detailed description of preferredembodiments, as illustrated in the accompanying figures. As will berealized, the invention is capable of modifications in various respects,all without departing from the invention. Accordingly, the drawings andthe description are to be regarded as illustrative in nature, and not asrestrictive.

BRIEF DESCRIPTION OF THE FIGURES

The above and other aspects, features, and advantages of the presentinvention may be more apparent from the following more particulardescription of embodiments thereof, presented in conjunction with thefollowing drawings. In the drawings:

FIG. 1 illustrates the downlink stage.

FIG. 2 illustrates the uplink stage.

FIG. 3 is a flowchart.

DETAILED DESCRIPTION

A better understanding of various features and advantages of the presentmethods and devices may be obtained by reference to the followingdetailed description of illustrative embodiments of the invention andaccompanying drawings. Although these drawings depict embodiments of thecontemplated methods and devices, they should not he construed asforeclosing alternative or equivalent embodiments apparent to those ofordinary skill in the subject art.

Referring to the accompanying drawings, and initially mainly to FIGS. 1and 2, there is illustrated an example of integrating downlink bearingbits and an uplink pay load and jointly encoding the downlink bits andthe uplink bits to form a combined bit stream to be sent in the uplink.

The present method and devices apply a principle of network coding wherebit streams coming from different nodes can be added together to improvethe overall system capacity. Such principle is particularly applied in ascenario of machine type communication (MTC) where coverage requirementscan be very challenging, especially for an uplink that is limited by themaximum transmitting power and the number of antennas at the terminals.The situation can be aggravated because uplinking terminals may bedevices such as utility meters installed in basements, from which goodtransmission is difficult to obtain. The situation of the downlink tendsto be less difficult, because the base stations can easily have highertransmitting power and a larger number of antennas than the terminals.Hence, some link budget imbalance between downlink and uplink can becompensated by jointly decoding the downlink and uplink signals.

In the example shown in FIGS. 1 and 2, only two terminals are shown, inthe form of mobile stations denoted as user equipment UE1 and UE2,respectively. However, there may be more or fewer terminals, and some orall of the terminals may be stationary rather than mobile.

Referring now also to FIG. 3, during a downlink transmission stage, thebase station sends signals bearing information bit streams d1 and d2 toterminals UE1 and UE2, respectively. These two streams can in general bedifferent, which means that they can be encoded and modulated withdifferent code rates and modulation order, and then transmitted to eachHE with dedicated resources. This provides the freedom to adjust thedownlink transmission payload individually to each mobile station. Sinceuplink quality of each mobile station may be different, the optimum sizeand content of the downlink payload to participate the joint coding maybe different for different uplink connections.

Alternatively, bit streams d1 and d2 can be the same, so that the basestation can broadcast to both UE1 and UE2, using the code rate,modulation, and radio resources common to them. While the broadcasttransmission has less flexibility in controlling the downlink data rateper link, it has less overhead and may be preferable in some scenarios.In a larger system with many terminals UE1, UE2, . . . , some or all ofthe terminals may be organized in groups with a common transmission toall the terminals in a group, and different transmissions to terminalsnot in the same group.

When a terminal UE1 or UE2 successfully decodes the respective bitstream d1 or d2, the terminal then encodes its own uplink payload, u1 oru2, respectively, jointly with the respective downlink payload d1 or d2,to form an uplink payload f(d, u). The joint coding can be a type ofnetwork coding. A very simple of such joint coding can be an “exclusiveor” operation on each bit of “d” and “u”. In this case, the length of“d” used in the coding is the same as the length of “u”. Consequently,the jointly coded bit stream has the same length as the terminal's ownuplink payload. If the length of the uplink payload is known in advance,then a downlink payload “d” of the correct length may be supplied.Alternatively, or if a common downlink payload is used by two or moreterminals having uplink payloads of different lengths, the downlinkpayload may be truncated or repeated to provide a bit stream of thecorrect length. Alternatively, a more sophisticated joint coding may beused and the resulted bit stream may be longer than the mobile's ownuplink payload.

At the base station's receiver, the uplink message is decoded. Thedecoder takes account of the downlink transmitted bit stream “d”, whichis of course already known to the decoder. The decoder also uses theknowledge of the joint coding mechanism at the terminal's transmitter,which is agreed in advance or specified in the air-interfacespecifications. The decoding is then performed in joint manner, where“d” also participates the decoding of “u”.

Many modifications and alterations of the methods and systems describedherein may be employed by those skilled in the art without departingfrom the spirit and scope of the invention which is limited only by theclaims.

1-20. (canceled)
 21. A method of wireless communication comprising,transmitting, by a base station to at least one of a plurality ofterminals, a downlink message comprising user-specific information toindividual ones of the plurality of terminals; receiving, by the basestation from the at least one of the plurality of terminals, an uplinkmessage encoded jointly with at least some of information in thedownlink message; and decoding the uplink message based on the downlinkmessage.
 22. The method of claim 21, wherein the user-specificinformation comprises at least one of a payload size, a modulationorder, a bit rate, a signal format, a channel coding, or atime-frequency resource that is different the individual ones of theplurality of terminals.
 23. The method of claim 21, wherein the uplinkmessage is encoded jointly based on performing a bitwise “exclusive or”operation on information in the downlink message and information in theuplink message.
 24. The method of claim 21, wherein the plurality ofterminals comprises machine type communication (MTC) devices.
 25. Awireless communication device, comprising: a transmitter configured totransmit, to at least one of a plurality of terminals, a downlinkmessage comprising user-specific information to individual ones of theplurality of terminals; a receiver configured to receive, from the atleast one of the plurality of terminals, an uplink message encodedjointly with at least some of information in the downlink message; and aprocessor configured to decode the uplink message based on the downlinkmessage.
 26. The device of claim 25, wherein the user-specificinformation comprises at least one of a payload size, a modulationorder, a bit rate, a signal format, a channel coding, or atime-frequency resource that is different the individual ones of theplurality of terminals.
 27. The base station of claim 25, wherein theuplink message is encoded jointly based on performing a bitwise“exclusive or” operation on information in the downlink message andinformation in the uplink message.
 28. The base station of claim 25,wherein the plurality of terminals comprises machine type communication(MTC) devices.
 29. A method of wireless communication, comprising:receiving, by a terminal from a base station, a downlink message that isuser-specific to the terminal; encoding an uplink message jointly withat least some of information in the downlink message; and transmittingthe uplink message that is jointly encoded to the base station.
 30. Themethod of claim 29, wherein at least one of a payload size, a modulationorder, a bit rate, a signal format, a channel coding, or atime-frequency resource of the downlink message is user-specific to theterminal.
 31. The method of claim 29, wherein encoding comprisesperforming a bitwise “exclusive or” operation on information in thedownlink message and information in the uplink message.
 32. The methodof claim 29, wherein the terminal comprises a machine type communication(MTC) device.
 33. A wireless communication device, comprising: areceiver configured to receive, from a base station, a downlink messagethat is user-specific to the terminal; an encoder configured to encodean uplink message jointly with at least some of information in thedownlink message; and a transmitter configured to transmit, to the basestation, the uplink message that is jointly encoded.
 34. The device ofclaim 33, wherein at least one of a payload size, a modulation order, abit rate, a signal format, a channel coding, or a time-frequencyresource of the downlink message is user-specific to the terminal. 35.The device of claim 33, wherein the encoder is configured to encode theuplink message jointly based on performing a bitwise “exclusive or”operation on information in the downlink message and information in theuplink message.